1. Field of the Invention
This invention relates to a rubber composition for tires having improved processability, wear resistance, rebound resilience and heat build-up.
2. Related Art Statement
As a polybutadiene used in the rubber composition for tire, there have hitherto been used high cis1,4 polybutadiene obtained by using a Ziegler catalyst, low cis-1,4 polybutadiene obtained by using a lithium catalyst, and the like. In these polybutadienes, it is difficult to simultaneously establish the processability and the vulcanization properties such as wear resistance, rebound resilience, heat build-up and the like.
Besides the above polybutadienes, polybutadiene obtained by emulsion polymerization process, polybutadiene recently obtained by using an alkaline earth metal catalyst and the like (Japanese Patent laid open No. 60-197,749) are known as a polybutadiene having a high trans-1,4 content. They are excellent in the processability, but are unsatisfactory in the vulcanization properties. Although the processability and the wear resistance are excellent, there is particularly a problem on the rebound resilience and heat build-up as the vulcanization properties.